A two-part permanent hair dye composed of the first part containing an alkaline agent and an acid dye intermediate and the second part containing an oxidizing agent has been broadly used for dyeing hair. The two-part permanent hair dye works in general according to a mechanism that the hair is dyed while it is bleached. The oxidizing agent contained in the second part works to generate a dye by an oxidative coupling reaction of the acid dye intermediate, and at the same time to lighten the hair by oxidatively decomposing melanin therein. The alkaline agent contained in the first part works to promote the dyeing action as well as the bleaching action by enhancing the activity of the oxidizing agent. Recently fashion hair coloring, namely enjoying a whole or part of the hair dyed in various colors, has been well accepted by consumers, while sufficient bleaching is required to dye the hair in a brighter color than the original hair color. Further, for coloring gray hair for masking, sufficient bleaching is required to achieve a brighter tone than the original hair color and to achieve a satisfactory masking effect. Since the bleaching activity on the hair depends on the quantity of the alkali and the oxidizing agent, when the hair dye is used for such purposes, large amounts of the alkali and the oxidizing agent are especially required.
Although as an alkaline agent ammonia and an organic amine, and as an oxidizing agent hydrogen peroxide are broadly used, if a large amount thereof is used in order to obtain sufficient bleaching activity, it may raise a problem that the hair is damaged or the scalp is irritated, depending on the amount used.
In some cases, persulfate having strong oxidizing activity is added as the third part in order to dye the hair very bright, in other words, to oxidatively decompose melanin thoroughly, which has, however, drawbacks that severe damage of hair proteins may be caused by the nonselective strong oxidation activity of the persulfate, and that, as another serious problem, the dye produced by the coupling is decomposed by the persulfate leading to a decrease in dyeability contrary to the intention.
Use of certain amines has been proposed to solve the problems (e.g. Patent Documents 1 and 2); however their performance has not been adequate for the bleaching performance required in recent years.
Use of some diazacycloheptanes in a bleaching agent for textiles as a bleaching catalyst has been known (Patent Documents 3 and 4). But the disclosure is limited to the use of diazacycloheptanes with manganese, etc. as metal complexes, and there has been no indication whatsoever about the use thereof in a two-part hair dye for hair.
[Patent Document 1] JP-A-2002-255763
[Patent Document 2] WO2003/051322
[Patent Document 3] WO2001/85717
[Patent Document 4] U.S. Pat. No. 6,537,959